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LED headlight swap won't stay on


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8 replies to this topic

#1 OFFLINE   okashira

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Posted 22 August 2015 - 04:49 PM

Tested out some LED headlights from ebay.

http://www.ebay.com/...=STRK:MEBIDX:IT

 

The LED's work fine and seem to put out good light.

 

Installed one to one side..

When I turn on the ignition, it lights for about two seconds, then turns off. The halogen side stays on.

 

I am guessing it is CANBUS problem, related to the current draw:

The car detects lower current then expected, then shuts off the light.

 

Strange thing is there are no errors on the instrument cluster showing bad headlight... Even if I remove the light and drive.

 

What is the best way to fix this without a parallel load resistor, which would defeat the purpose of installing an LED...









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#2 OFFLINE   Automate

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Posted 23 August 2015 - 09:51 AM

Interesting question.  Most people solve the problem by installing the parallel load resistor but I agree, that defeats the purpose of using a low wattage LED bulb.

 

Here is a simple bulb monitoring circuit that uses a relay

My guess would be that Ford uses something more advanced than this but I don't know for sure.

 

Maybe they use a circuit something like this

http://www.eeweb.com...-car-lampsbulbs

 

In any case there is probably a resistor somewhere in the existing circuit (maybe part of a voltage divider)  that determines the amount of current which will satisfy the bulb monitoring circuit.  But finding the proper resistor and replacing it with another value may not be easy.

 

Worst case you could temporarily install a variable resistor in parallel with the bulb and then adjust its  value to determine the maximum resistance which does not trip the bulb detection circuit.  Then you could install a fixed resister with the same value as the variable resistor 

 

 


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#3 OFFLINE   okashira

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Posted 23 August 2015 - 10:05 AM

Interesting question.  Most people solve the problem by installing the parallel load resistor but I agree, that defeats the purpose of using a low wattage LED bulb.

 

Here is a simple bulb monitoring circuit that uses a relay

My guess would be that Ford uses something more advanced than this but I don't know for sure.

 

Maybe they use a circuit something like this

http://www.eeweb.com...-car-lampsbulbs

 

In any case there is probably a resistor somewhere in the existing circuit (maybe part of a voltage divider)  that determines the amount of current which will satisfy the bulb monitoring circuit.  But finding the proper resistor and replacing it with another value may not be easy.

 

Worst case you could temporarily install a variable resistor in parallel with the bulb and then adjust its  value to determine the maximum resistance which does not trip the bulb detection circuit.  Then you could install a fixed resister with the same value as the variable resistor 

 

You are right. If the system is measuring current to shut off the bulb, there must be a shunt resistor somewhere. Ideally one could simply replace this resistor with one of higher resistance.

But finding the resistor would not be easy. I don't have the service manual yet, but perhaps a clue is in there. It could be near the ECU, near an ignition relay,or on the headlight circuit itself.

 

Another idea is to try both LED's on one side of the circuit. Hopefully two in parallel will pull enough current as to not piss off the sensor.


Edited by okashira, 23 August 2015 - 10:07 AM.


#4 OFFLINE   okashira

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Posted 23 August 2015 - 11:40 AM

went ahead and tried two in parallel on one side. didn't work.

 

With only one LED connected:

1. with DRL on, igniton on, LED flashes for about 0.5 seconds then off

2. with HL on,ignition on, LED flashes for about 2 seconds then off

 

with two in parallel

1. both DRL and HL, LED's flash for about 0.5 seconds then off

 

Very strange

 

If someone has a service manual wiring diagram, any hints as to headlight sensor location ?



#5 OFFLINE   jdbob

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Posted 23 August 2015 - 12:38 PM

The current source would be in the BCM (Body Control Module). It might be a resistor, or it might be a current source. In the case of the license plate bulbs I found the BCM was supplying about 1ma. Without a resistor there was 5V across the LED bulb (due to voltage drop in the LED's themselves as well as the diode-bridge to make sure you could plug the bulb in either way). I put a 2K 1/4W resistor and that dropped the voltage down to 2V at which point the car was happy.

 

In the case of the headlights, which are much more important than license plate bulbs, they may be measuring the current draw with the bulbs on instead of just the simple voltage check when they are off. As Automate said, you might just have to try lower and lower value resistors until you get it to work. If you do find a value that won't make the use of LED's pointless, drop the resistance another 20% or so to make sure it stays working.



#6 OFFLINE   komondor

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Posted 24 August 2015 - 06:07 PM

usually the DRL is just sending lower voltage, the leds are not dimmable so that is probably part of the issue.

 

I would look at getting something like this

 

http://www.amazon.co...40467467&sr=8-7



#7 OFFLINE   jdbob

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Posted 24 August 2015 - 06:31 PM

usually the DRL is just sending lower voltage, the leds are not dimmable so that is probably part of the issue


Edited by jdbob, 24 August 2015 - 10:30 PM.


#8 OFFLINE   okashira

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Posted 25 August 2015 - 10:10 AM

usually the DRL is just sending lower voltage, the leds are not dimmable so that is probably part of the issue.

 

I would look at getting something like this

 

http://www.amazon.co...40467467&sr=8-7

 

LED are actually very dimmable, but in the form I am using them (12V supply with their own driver,) they may not be

That might be part of the problem.

 

I think the car uses PWM to dim the headlights.

DRL's are set for 66% and with headlights on 90%.

PWM could be a problem for the LED driver circuit..

 

I may just have to wire in a separate ignition switched 12v source. I think that's the best solution for now...



#9 OFFLINE   okashira

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Posted 27 August 2015 - 05:42 PM

More investigation

 

http://fordcmaxhybri...cussion/page-5?










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